The present invention relates to pumps used for the production of undergound reservoir fluids, in particular to electric submersible pumps used in the production of reservoir fluids such as crude oils.
An electric driven submersible pump used for the production of crude oil normally comprises an electric motor at the bottom of the apparatus and a multiple stage centrifugal pump at the top. The suction inlet for the pump is normally located about the mid-point of the overall apparatus and the discharge is at the top apparatus. This permits the pump to be attached to the normal production tubing string and lowered into the well together with the electric cable for transmitting power to the motor. As the pump is lowered, cable is strapped to the production tubing string. Operations are designed to minimize tubing manipulation to reduce the risk of cable damage. In wells that are producing relatively sweet crude oils, or other non-corrosive fluids this system works satisfactorily. In many cases, the production tubing/production casing annulus is used to vent solution gas which is produced along with crude oils. In the case of wells that contain sour crudes or other fluids (i.e., CO.sub.2) that are corrosive, steps must be taken to protect the pump and the casing in the well. The normal procedure is to provide a packer above the pump so as to isolate the well fluids from the annulus between the casing and tubing. While this is a possible solution, it does involve considerable difficulty, since the electrical conductors must be passed through the packer and some means must be provided for seating and unseating the packer in the well.
Attempts to utilize this system are normally dependent on hydraulically set packers which can be set and released by hydraulic pressure or other packers which do not require tubing rotation for setting or releasing. While this is a possible solution, these type of packers normally are difficult to unseat and remove from wells producing corrosive fluids. Thus, when it is necessary to remove the pump from the well for servicing, considerable difficulty is involved in trying to unseat the packer and retrieve it so that the pump can be removed.